Tires, conventionally, are produced by forming or "laying up" of uncured or so-called green tire components on a tire building machine. The resulting green tire is then removed from the tire building machine and placed into a tire mold. The tire mold generally is configured to apply heat and pressure to the green tire forcing the green tire to conform to the configuration of a cavity within the tire mold, and through curing, retain that desired configuration. It is desirable that the cured tire conform quite closely to the configuration established by the tire mold, and such conformance is in significant measure dependent upon avoiding air entrapment between the green tire and molding surfaces of the mold.
Conventionally, the presence of air between the green tire and molding surfaces of the mold during molding operations is substantially precluded by the provision of a substantial plurality of small-bore passages or apertures extending from molding surfaces of the mold through the structure of the mold to points external to the mold. Thus, as the green tire is moldingly forced into close conformance with molding surfaces of the mold, air entrapped between the green tire and molding surfaces of the mold tends to be forced from the mold cavity via the apertures or passages. These apertures or passages conventionally are termed "vents".
While such vents typically provide for an acceptable evacuation of air from the mold, green or uncured rubber forming a portion of the green tire being molded enters these vents subsequent to entrapped air having been forced from the mold. This green rubber cures within the vents, remaining attached to the tire being molded after curing, so that when the mold is opened, and the cured tire is removed, these vents provide a plethora of needle like projections protruding generally perpendicularly from the surface of the cured tire. These projections are also termed "vents" conventionally and provide the tire with an external appearance generally regarded as objectionable.
Such protrusions or projections protruding from the cured tire generally are removed by placing the tire on a machine whereby the finished, cured tire can be spun, and cutting, either automatically or by hand labor, these projections from the tire. Termed "vent trimming", this projection cutting procedure typically adds to the manufacturing cost of the finished cured tire and results often in the generation of a significant quantity of waste or blemished tires where the trimming operation goes awry, producing a cut or surface blemished tire. In addition, after vent trimming, the tire surface remaining often is considered to be possessed of a general, overall unattractive appearance.
It has been suggested that were air to be removed from the mold cavity employing a vacuum during the molding process, the necessity for at least some mold vents may be obviated. Accordingly, in one proposal exemplified by U.S. Pat. No. 1,276,411, a plurality of tire molds were placed within a large press cavity, and the press cavity was evacuated thereby evacuating the plurality of molds. The press was then actuated to compress the molds within the cavity in order to form finished tires.
In another proposal exemplified by U.S. Pat. No. 2,779,386, vacuum was introduced to the mold along a mold parting line and the tread portions and ply portions of the green tire were punctured so as to create air pathways from a zone adjacent an interface between the tire interlayer and the carcass of the tire to remove any entrapped air from this zone.
In still another proposal exemplified by U.S. Pat. Nos. 4,347,212; 3,842,150; and 3,854,852, a plurality of valves were positioned embeddedly within the mold along, particularly, sidewall portions of the mold. The valves in this proposal were configured to open as the mold closed, and to evacuate air from within the mold as the green tire was pressed against the molding surfaces of the mold. The valves were configured, hopefully, to close before being contaminated with rubber forced into the valves during the molding process. Each valve was connected to a source of vacuum so as to provide for evacuation of the mold. Others have employed poppet valves in tread but not sidewall portions of the mold.
In yet another proposal exemplified by U.S. Pat. No. 3,983,193, green tire portions being applied in a retreading operation have been surrounded with an elastomeric bag having a vacuum suction port whereby a vacuum cavity may be created surrounding the tire being retreaded.
The foregoing proposals have generally failed to meet with commercial success for a variety of reasons. Where a plurality of molds are contained within an evacuated press for molding, time constraints associated with assembling and disassembling molds containing green tires for introduction into a hydraulic press has generally proven excessively costly. For processes wherein vacuum is drawn along a parting line to evacuate, particularly interior interfaces of portions of the green tire carcass, a failure to achieve a significant, reliably effective vacuum has contributed to commercial disinterest in such processes. Where a plurality of poppet type valves are employed positioned for example along a sidewall portion of a tire mold, difficulties in evacuating tread portions of the mold frequently have resulted in the production of an unacceptably elevated number of less than acceptable quality tires. In processes wherein a polymeric bag surrounds a green tire portion being appled as a retread, difficulties in assemblying and disassembling such a bagged green tire has contributed substantially to commercial disinterest.
A process wherein a quality tire is produced without the necessity for providing vent holes or so-called vents in a tire mold reliably and without significant extension to the processing cycles of existing tire mold presses could find substantial utility in the commercial manufacture of tires by elimination of costly tire vent trimming and by savings of rubber otherwise lost in the vent trimming operations.